Many image compression coding techniques have been proposed since a storage medium having a very large size is required to save an image with high resolution and high pixel precision as a raw image.
For example, a technique for saving/transferring X-ray medical images in an electronic format, and using them in diagnosis has been proposed. In the medical field, images preferably have highest possible resolution, and an effective image compression method is demanded.
On the other hand, various techniques for canceling noise appearing in images have been proposed and are used in various fields.
However, no technique for effectively reducing noise in the image encoding/decoding process has been proposed yet.
For example, in an image sensing device using X-rays, the X-ray dosage upon image sensing is preferably as small as possible in consideration of the influences on a patient. But an image sensed with a small X-ray dosage contains many quantization noise components, which disturb diagnosis. As a method of reducing such quantization noise in a medical image, a method that exploits multiresolution analysis is known, as disclosed in Japanese Patent Laid-Open No. 09-212623. According to this technique, it is possible to remove noise based on the multiresolution analysis result of an image. However, in order to incorporate such method in a conventional apparatus, a noise removal process must be added. Also, when this method is combined with image coding, flexible adjustment of image quality is disturbed upon display.